The reason given was that rice exporters of Vietnam have not fully met US market regulations, particularly in terms of food safety hygiene and pesticides.
According to processing and exporting companies in the Mekong Delta, this move almost closed the door for the export of Vietnamese rice grain into the US. At present, Vietnam exports about 5,000 tonnes of rice to the US annually.
Even though small in quantity, high value has proved worthwhile / with each tonne in the US having average prices $100 to $200 higher than other markets.